1. Field of the Invention
The present invention relates generally to software-defined communications devices, and particularly to the calibration of device communications signals in a manner that maximally decouples device software from device hardware, simplifies device design, reduces device cost and enhances device software portability.
2. Description of Related Art
Conventional open architecture software-defined communications systems operating on a network, such as a TDMA or frequency hopped network, enable system hardware and software components to be added, removed or upgraded on an as-needed basis. Such systems therefore provide both system users and designers with a high degree of flexibility in adapting to changing communication needs and demands.
Radios utilized in open architecture software-defined communications systems must transmit signals at precise times in order to be compatible with network signal transmission protocol. Because these signals often have associated system hardware delays and/or external propagation delays, conventional radios must typically include timing circuits or microprocessor timers to compensate for the delays when the signals are demodulated.
However, such conventional signal delay compensation techniques have limitations. For example, the above-mentioned timing circuits require that specialized hardware be added to each radio to generate delay-compensation interrupt timing signals. The required timing circuit components must be designed to compensate for a specific type of waveform, thereby limiting the use of the radio only to reception of signals that are compatible with the timing circuits. The additional required hardware components for the circuits also increase the overall cost of each radio.
Further, the accuracy of microprocessor timers is directly related to the corresponding microprocessor clocks. Commercial microprocessor card vendors commonly utilize low cost crystal oscillators to drive microprocessor clocks. Because crystal oscillators are subject to frequency drift over time and due to fluctuations in temperature, the accuracy of such timers in compensating for modulation delays is often limited. In addition, numerous types of microprocessor timers with varying degrees of precision are commercially available. Therefore, as the resulting demodulator accuracy depends on the specific type of microprocessor, systems incorporating such timers for signal delay compensation must be designed for use with a specific microprocessor timer.